a) Field of the Invention
The present invention relates to a core-board of improved structure, which is particularly well, although not exclusively, designed for use as a floor panel in a railroad wagon.
The invention also relates to the core used in this core-board, and to the way such core-board may easily yet efficiently anchored and/or rigidly connected edge-to-edge to adjacent core-boards.
b) Description of the Prior Art
Core-boards (also known as sandwich panels) are well known products. As shown in FIG. 1 which is illustrative of the prior art, the most conventional core-boards comprise a core 53 usually of honey-comb structure that is sandwiched between two flats outer panels 55, 57, hereinafter called "skins", that are glued to the core. Depending on the application, the core can be made of a composite material or another light weight material such as aluminum. Similarly, the skins can be made of any desired material.
If these known core-boards are very strong and resistant to compression forces applied in the direction shown with the arrows A in FIG. 1, they are rather weak when shearing forces are applied to them in the directions shown with the arrows B in the same Figure.
To overcome this deficiency, it has already been suggested to use cores that are tridimensional and consist of a thin panel having a plurality of bosses or cells of identical or different shapes, that project from both sides thereof. See, for examples, U.S. Pat. Nos. 2,809,908; 3,622,430; 3,940,811; 4,025,996; 5,156,327; 5,242,735 and 5,266,379. The cores disclosed in these patents overcome at least in part the above mentioned deficiency of the honey-comb shaped cores. However, they are still open to improvements.
It is also of common practice to use core-boards as floorings in cars or locomotives in the railway industry. To be efficient for such application, the core-boards must satisfy a plurality of very specific requirements.
First of all, the core-boards must be structural and have thermic insulation properties that meet with the very specific provisions of the flame exposition duration standard ASTM E 119.
The core-boards must also be of such a design that one may cut them as wanted to install them whenever required in a wagon.
The core-boards must further be strong enough to be bolted onto the frame of a railroad car and to allow fixation of passenger seats.
The core-boards must be capable of receiving an antiskidding surface coating.
Last of all, the core-boards must be light, rigid and strong enough to resist the stresses to which any car flooring is subjected. In the meantime, they must also be economically competitive with the presently available materials.
It is quite obvious that the critical element of any core-board is the core of it. Indeed, for a very specific application like the one mentioned above the core must satisfy the following requirements:
High compression and tension resistance; PA1 High shearing and impact resistance; PA1 High rigidity and low fragility; PA1 High thermic resistance; PA1 Excellent flexion, vibration and stress resistance; PA1 High dimensional stability under thermic or chemical stresses; PA1 Minimum crack growth during cutting or piercing; PA1 Lightness, rapidity of assembly and dimensional uniformity; and PA1 Simple yet versatile geometry. PA1 a central surface extending in a plane; PA1 a plurality of embossments hereinafter called "top cells", that are identical in shape and project from the central surface on one side thereof; and PA1 another plurality of embossments hereinafter called "bottom cells", that are identical in shape and project from the central surface in a direction opposite to the top cells. PA1 it is of modular structure and easy to manufacture; PA1 it is very strong and resistant to compression, tear-out and shear forces; PA1 it is also very resistant to torsion and vibration; PA1 anchoring means can be inserted therein at any desired location; PA1 the distance between the anchoring means can be very short; PA1 cutting of it is quite easy to do.
Researches carried out by the Applicant to find a core-board geometry allowing installation of the same without any limitation on any kind of supporting car frames, have shown that core-boards having cores of the molded or formed type are capable of satisfying the above-mentioned requirements. These cores are made by molding of a polymer resin with a reinforcing material such as fibers. Such cores advantageously allow the insertion of inserts for anchoring purpose.
In this connection, it is worth reminding that among all the characteristics that a core-board must satisfy to be useful as a car flooring, its ability to receive anchors is a very important one. Indeed, the cantilever force applied by the passenger seats onto the anchors inserted into the flooring in the case of an impact may cause the core-board to be torn out of the frame of the wagon to which it is connected.
Under such conditions, a shearing effect may be generated, which may cause the opposite skins of the core-board to delaminate, especially if the fixation of the core-board to the frame has not been made with bolts passing through the entire thickness of the core-board.
Accordingly, there is presently a need for a core-board which not only would satisfy the above mentioned requirements but also would allow anchoring of the same to a supporting frame or anchoring of equipments such as passenger seats onto the core-board in an efficient, shear resistant manner while avoiding the formation of thermal bridges.